Question

Can anyone give me running notes of how do organisms reproduce plz I am need

Answer 1

Introduction

→ Reproduction is the process by which living organisms produce new individuals similar to themselves. It ensures continuity of life on earth.

→ Nucleus of the cell contains DNA (Deoxyribose Nucleic Acid) which is the heredity material.

→ DNA replicates and forms new cells causing variation. So, these new cells will be similar but may not be identical to original cell.

→ Variations are useful for the survival of the individual and species over time as well as basis for evolution.

Types of Reproduction

Asexual Reproduction

→ A single individual give rise to new individual.
→ Gametes are not formed.
→ New individual is identical to parent.
→ It is extremely useful as a means of rapid multiplication.
→ Adopted by lower organisms.

Sexual Reproduction

→ Two individuals i.e., one male and one female are needed to give rise to new individual.
→ Gametes are formed.
→ New individual is genetically similar but not identical to parents.
→ It is useful to generate more variations in species.
→ Adopted by higher organisms.

Modes of Asexual Reproduction

Fission

→ The parent cell divides into daughter cells.

• Binary fission: 2 cells are formed. Example: amoeba.


• Multiple fission: Many cells are formed. Example: Plasmodium.


Fragmentation

→ The organism breaks-up into smaller pieces upon maturation, each piece develops into new individual. Example: Spirogyra.


Regeneration

→ If organism is somehow cut or broken into many pieces, each piece grows into a complete organism. Example: Planaria, Hydra.


Budding

→ A bud is formed which develops into tiny individual. It detaches from parent body upon maturation and develops into new individual. Example: Hydra



Vegetative Propagation

→ In many plants, new plants develops from vegetative parts such as:

• By roots: Example: dahlias, sweet potato.

• By stem: Example: potato, ginger.

• By leaves: Example: bryophyllum (leaf notches bear buds which develop into plants).



Artificial methods in Vegetative Propagation

(i) Grafting: Example: Mango

(ii) Cutting: Example: Rose

(iii) Layering: Example: Jasmine

(iv) Tissue culture: New plants are grown by using growing tip of a plant.

→ These growing cells are kept in a culture medium leads to the formation of callus. Callus is then transferred to hormone medium which causes growth and differentiation.
Example: ornamental plants, orchid.

• Benefits of tissue culture

→ We can grow plants like banana, rose, jasmine etc. that have lost the capacity to produce seeds.
→ New plants are genetically similar to parents.
→ Helps in growing seedless fruits.

(v) Spore Formation: Spores are small bulb like structures which are covered by thick walls. Under favourable conditions, they germinate and produce new organism.
Example: Rhizopus


Sexual Reproduction

→ When reproduction takes place as a result of the fusion of male and female gametes is called sexual reproduction.

→ Fusion of gametes is called fertilization which results in variation.

Sexual Reproduction in Plants

→ Flowers are the reproductive organs of plants.

→ A typical flower consists of four main whorls namely sepals, petals, stamen and pistil.

Types of Flowers

• Bisexual flower: Both male and female reproductive parts are present.
Example: Hibiscus, mustard.

• Unisexual flower: Either male or female reproductive part is present.
Example: Papaya, watermelon.

Structure of Flower


Process of Seed Formation

→ Pollen grains, produced in the anther, are transferred to the stigma of same flower (self pollination) or stigma of another flower (cross pollination) through agents like air, water or animals.

→ Pollen grains germinate and form pollen tubes which pass through style to reach upto the ovules present in ovary.

→ The fusion of male and female gametes is called fertilization. Zygote is produced inside the ovary.

→ Zygote divides to form embryo. Ovule develops thick coat and changes into seed gradually.

→ Ovary changes into fruit and other parts of f